NAD 3400 recap

[Oggioffshore]

Hi.
Looking to do a recap job on one of my3400's

Anyone done this? And what was the outcome, improved sound?
I'm rusty in reading schematics, but guess you just change the capacitors along the signal way with same values...

Just think after 30 "years, it can't harm.

Cheers

 

[Bradbrews]

I rebuilt my 3300 and feel it provided a worthwhile improvement.

I've had my NAD 3300 Integrated Amp since it was new. Other than having drop-outs at low volume due to the troublesome speaker relays (now replaced) it's been a rock solid performer for ~3 decades. A while back I restored some Dynaco MKIII's and given that they are just amps, decided to use the NAD's preamp to drive them. I did this for a few months and was underwhelmed with the MKII's. Nothing worng with them, but not really the difference I thought there would be vs the NAD itself.
Then I built a passive pre-amp (just a POT) and used it instead of the NAD for the MKIII's. WOW - that was the big difference. It sounded like a veil was pulled off of the sound and there was a lot more detail, more crisp highs, harder hitting, less muddy bass. wow. Having gotten into tubes, I then rebuilt a Scott LK-72. Again, sound very similar to the MKIII's, but the Scott has a preamp being an integrated.
So all of this has led me to believe that over the last 30 years, the preamp in the NAD 3300, which is the same as the NAD 1300 preamp I'm led to believe, has gotten a bit dull in the last few decades. This unit always ran quite hot, and I rocked it pretty hard for a long time. Back in the Bachelor days I had to have a fan blowing across it to keep it from gong into thermal shutdown..
So now I'm thinking about re-caping the preamp - to start with. I've attempted to identify the electrolytic caps in the signal path - there seem to be a Lot of them. In the attached file the ones I think are in the path are highlighted yellow. The others I suspect are not in the path.
How did I do?

 

[Oggioffshore]

Cheers.
Saw u wrote u put out schematics with the caps marked out?

 

[Bradbrews]

If you click the little arrow in the quote it takes you to the thread. There is more info there. I ended up replacing all the electrolytics except the main filters, which tested good. I also replaced the speaker relays, which was the main problem, along with a multitude of cracked solder joints that needed reflowing.

 

[Buanadha]

Hi.
Looking to do a recap job on one of my3400's

Anyone done this? And what was the outcome, improved sound?
I'm rusty in reading schematics, but guess you just change the capacitors along the signal way with same values...

Just think after 30 "years, it can't harm.

Cheers

haven't done this myself, but I have a 3400 and a 7400 around that might be candidates for a recap.

Want to hear how yours sounds when you finish!

 

[Oggioffshore]

Hi, I`ll get back when its done.
The challenge is to read out which caps to change, and get the time to do it .

 

[Oggioffshore]

cheers, i look into it. and get some ideas .

 

[Oggioffshore]

Some updates.

Have managed to recap 3 of these 3400's by now... And a 1600 pre amp.

The first 3400 I'll put in bigger main filter caps, changed the op amps. ... Maybe mentioned earlier, but I've also put in thicker wires from relays to speaker terminals and changed the original terminals to "better" ones...
Amplifier sounds great, if it sounds better I'm not sure. Feels like it does.

2nd 3400, have some distorted cracking sound after playing a while.. Haven't found what causes this.. Sprayed and cleaned all switches and pots..
Same symptoms if only using pwr amp part with pre amp.... Have not recapped this one.

3rd 3400, I've got as a faulty unit. But when testing it plays good. Only had some white noise on the R channel... So I had caps leftovers and recapped it. Same noise. Started to swop transistors around, and some diodes.. It's quiet for now.

4th is replaced to our summer house. Plays good after recap, wire and terminal mods...

Have a small challenge with a 2400, that suddenly went into protection. Measuring 70 volts around every tr in one channel.... Hm. Gonna be Winther challenge in the cave...

Just received a 2400, 5000 & 1700 in the mail... Exited to check them out.

What's the main difference between 1600 & 1700 per amp?

Have a good one

 

[Oggioffshore]

haven't done this myself, but I have a 3400 and a 7400 around that might be candidates for a recap.

Want to hear how yours sounds when you finish!

It feels more punchy, and better bass.
Still somehow a little hard in the upper mids... Guess it can relate to the speakers as well... I don't have so many amps to compare with, but I had a HK 670 and i like the nad better.... More punch and fun listening to...

 

[BrassTeacher]

I've worked on a bunch of older NAD equipment, mostly the 3020. It's been my experience that what you describe is either caused by a bad solder joint that slowly heats up and becomes intermittent, or a dying semiconductor. If on both channels, look to the voltage regulator section. If channel specific, check the affected channel. The best way to check for dying semiconductor is to use freeze spray. You aim the little straw at a semiconductor, give a quick burst, and listen to see if there is a sudden change for the better. It's even more helpful to listen while observing the signal on an oscilloscope. Now a real can of freeze spray can get expensive, so an alternative if you are very careful is using a normal can of electronics "duster". Invert the can while using to get the freeze spray effect. This method is not remotely as accurate or controllable as a can of freeze spray, but it will work. You must be cautious, as too much spray from the "can of air" will cause moisture to condense on the component and surrounding area. That usually does not work well with electrical gear while powered up...

2nd 3400, have some distorted cracking sound after playing a while.. Haven't found what causes this.. Sprayed and cleaned all switches and pots..
Same symptoms if only using pwr amp part with pre amp.... Have not recapped this one.

 

[Oggioffshore]

I've worked on a bunch of older NAD equipment, mostly the 3020. It's been my experience that what you describe is either caused by a bad solder joint that slowly heats up and becomes intermittent, or a dying semiconductor. If on both channels, look to the voltage regulator section. If channel specific, check the affected channel. The best way to check for dying semiconductor is to use freeze spray. You aim the little straw at a semiconductor, give a quick burst, and listen to see if there is a sudden change for the better. It's even more helpful to listen while observing the signal on an oscilloscope. Now a real can of freeze spray can get expensive, so an alternative if you are very careful is using a normal can of electronics "duster". Invert the can while using to get the freeze spray effect. This method is not remotely as accurate or controllable as a can of freeze spray, but it will work. You must be cautious, as too much spray from the "can of air" will cause moisture to condense on the component and surrounding area. That usually does not work well with electrical gear while powered up...

In this case, I think /feel like it's a mechanical thing, but doesn't seem to help spray /clean the typical switches ...
So will try the freeze method later on...
Not sure of its a component failure, it's similar in both channels, indipendent on which output I use. A or B speakers, hence different relays.. Have been over all solder points...